Vitamin consumption and the ontogenesis of cathepsins and antioxidant capacity in developing embryos of turbot, Scophthalmus maximus

During embryonic development, vitamins are involved in energy metabolism and protein synthesis, while cathepsins and antioxidant defense play key roles in yolk degradation and protecting fish embryos from oxidative damage. This study aimed to investigate the consumption of vitamins (A, B₁, B₂, C, D, and E), ontogenesis of cathepsins, and antioxidant capacity in developing embryos of turbot. In this study, embryos were collected over time from 2.3 to 102.5 h (i.e., hatching) after fertilization for vitamins, cathepsins, and antioxidant capacity analyses. Results showed that the embryonic growth rate in the cleavage stage (CS) was faster than in other stages, while that in the segmentation stage (SS) was lower than in other stages. Embryos displayed higher demands on V_A during blastula stage (BS), gastrula stage (GS), the early SS, and hatching day (HD), V_B1 at CS; V_B2 at BS, GS, SS, and HD; V_D at CS and SS; V_E at CS, BS, and the late SS; and V_c during entire periods. Cathepsins A (CA) showed a high level at early SS, suggesting its involvement in yolk degradation. Cathepsins B (CB) and cathepsins D (CD) were highly active at GS, suggesting an active apoptosis process. CA, CB, CD, and cathepsins L (CL) all kept low levels in CS, revealing low protein demand during the cleavage process. On the whole, the predominant antioxidant enzymes were superoxide dismutase (SOD) and malondialdehyde (MDA) from CS to SS; SOD, MDA, glutathione peroxidase (GSH-Px), and catalase (CAT) during SS; and GSH-Px and CAT during HD. In conclusion, the fastest growth rate and the slowest growth rate of embryos occurred in CS and SS, respectively, being consistent with energy allocation. Vitamin consumption and cathepsin ontogenesis were stage-specific. Oxidative damage on embryos was relatively less at CS, but larger at SS and HD.